Disruption of PIP₂ prevents recruitment of WASP and decreases actin polymerization. IL-15–activated splenic NK cells were treated (+) or not (−) with 20μM m-3M3FBS and allowed to bind to ICAM-1–coated beads. (A) Cells were fixed, permeabilized and stained for PIP₂, and analyzed by confocal microscopy as in Figure 1. (B) Fluorescent intensity of PIP₂ staining was measured by drawing a line from the point of contact between an untreated NK cell bound to a PLL–coated bead (left), an untreated NK cell bound to an ICAM-1–coated bead (center), or an m-3M3FBS–treated cell (right). (C) Cells were fixed, permeabilized, stained for talin, actin, or WASP, and images were analyzed by confocal microscopy as in Figure 1. (D) Fluorescence intensity of staining at the contact site between an untreated (▬) or treated (▭) NK cell bound to an ICAM-1–coated bead expressed as a ratio of fluorescence at the contact site over fluorescence at a random point opposite. Error bars indicate SEM, n = 10 per condition. ***P < .005 and **P < .01 compared with corresponding PLL condition.